1. Field of the Invention
The present invention relates to an electrostatic chuck and a substrate fixing method using the same. More specifically, the present invention relates to an electrostatic chuck which holds, and fixes, a substrate subject to a treatment in a vacuum processing apparatus such as a charged particle beam exposure apparatus, and to a substrate fixing method using the electrostatic chuck.
2. Description of the Prior Art
With regard to a low pressure processing apparatus, such as a deposition apparatus by use of low pressure CVD and sputtering, an etching apparatus and an electron beam exposure apparatus, which performs a process under a low pressure, electrostatic chucks have been used as means for holding a substrate to be processed in many cases.
An electrostatic chuck to be used in a deposition apparatus has been disclosed in Japanese Patent Laid-open Official Gazette No. Tokkai 2001-77184 (hereinafter referred to as “Patent Literature 1”). FIG. 1 of Patent Literature 1 shows the inside of the main body 21 of the electrostatic chuck 20. A positive electrode 23 is provided in the entire surface of the left half plane, and a negative electrode 24 is provided in the entire surface of the right half plane. A substrate 111 with a uniform thickness on which an insulating film and the like are going to be formed is placed and held on the electrostatic chuck 20, as shown in FIG. 6 of Patent Literature 1.
Incidentally, Japanese Patent Laid-open Official Gazette No. Tokkai 2001-118776 (hereinafter referred to as “Patent Literature 2”) and Japanese Patent Laid-open Official Gazette No. Tokkai Hei. 10-50584 (hereinafter referred to as “Patent Literature 3”) have respectively disclosed electrostatic chucks which are used in charged particle beam exposure apparatus, although neither of these electrostatic chucks hold a substrate which was going to be processed. Each of these electrostatic chucks holds a mask substrate, which has a partially thicker portion and a partially thinner portion, and whose thinner portion has already been patterned. The electrostatic chuck according to Patent Literature 2 opens in its center portion corresponding to the thinner portion 107 of the mask substrate 101 which has been placed, and arc-shaped electrodes 103 and 103′ or half ring-shaped electrodes 503 and 503′ are embedded in a belt-shaped peripheral portion corresponding to the thicker portion of the mask substrate 101, as shown in FIGS. 1 and 5 of Patent Literature 2. The electrostatic chuck according to Patent Literature 3 opens in its portion corresponding to the thinner portion 1b of the mask 1 which has been placed, and electrodes 4a are embedded in grid shape in its portions 2a and 2c corresponding to a thicker beam 1a and a frame 1c of the mask 1.
In general, a low pressure processing apparatus including the electrostatic chuck according to Patent Literature 1 can process not only a substrate with a uniform thickness, but also a mask substrate (a membrane mask substrate) which have a partially thicker portion and a partially thinner portion, while operating as a single apparatus.
For example, in a case where a membrane mask substrate is fabricated by use of an electron beam exposure apparatus including an electrostatic chuck which is similar to that disclosed in Patent Literature 1, a resist film is formed in a plane surface of a substrate which has a partially thicker portion and a partially thinner portion. The substrate is placed on the electrostatic chuck in a way that the back surface of the substrate, on which the resist film has not been formed, and which is the back surface of the thicker portion of the substrate, is brought into contact with the substrate placement surface of the electrostatic chuck. Then, voltage is applied to the electrodes in order to electrostatically adsorb, and fix, the substrate to the substrate placement surface of the electrostatic chuck. Subsequently, a resist film on a portion where the thickness of the substrate is thinner is exposed to light, and the resist film is developed. Accordingly, a resist pattern is formed in the substrate. Thereafter, the substrate is transferred from the exposure apparatus to an etching apparatus in a low pressure atmosphere by use of transfer means such as a robot. An opening is formed in the portion where the thickness of the substrate is thinner by using the resist pattern as a mask, and thereby a mask substrate is fabricated.
However, in a case where an electron beam exposure apparatus including the electrostatic chuck similar to that disclosed in Patent Literature 1 is applied to the membrane mask substrate, electrostatic attraction also acts in the portion where the thickness of the membrane mask substrate is thinner, since an electrode of the electrostatic chuck exists below the portion where the thickness of the membrane mask substrate is thinner. For this reason, it is likely that the portion where the thickness of the membrane mask substrate is thinner will deflect so that the flatness of the surface is deteriorated. Accordingly, it is likely that the precision in light exposure will be lowered.
For the purpose of avoiding the problems, there is a case that uses an electrostatic chuck similar to that disclosed in Patent Literature 2 including arc-shaped electrodes or half ring-shaped electrodes, which causes electrostatic adsorption force to act only on the portion where the thickness of the membrane mask substrate is thicker in order to fix the membrane mask substrate. In this case, however, it is likely that electrostatic adsorption force to the substrate with a uniform thickness will become insufficient, since an area where the membrane mask substrate is adsorbed to the substrate placement surface of the electrostatic chuck is small in spite of the relatively heavy weight of the substrate.
Alternatively, electrostatic chucks may be changed, when deemed adequately, depending on difference in shape of substrates, while those electrostatic chucks are used in the same single apparatus. However, the changing of the electrostatic chucks causes considerable inconvenience, thus lowering the throughput.